Panic! RAID 5 failed – what to do?

What is the best way to recover data after RAID 5 fails?

Storage is a crucial point when it comes to setting up a server. What kind of server you should use depends on your needs based on current and future plans. If your needs are uncomplicated, the single disk should be enough, but if you are searching for advantages like data storage redundancy in combination with a high level of performance, you should think about RAID as a solution.

RAID 5 is among the other RAID levels, one of the most common used solutions. It consists of three or more hard drives with the same capacity. Three hard drives are minimum for RAID 5, and it is an advantage if all of them are the same capacity. If not, the RAID controller will establish the RAID 5 volume taking into consideration the lower capacity of hard drive. This RAID array uses a combination of striping and parity techniques.

  • Striping – the way of splitting the flow of data into blocks of a certain size and writing blocks across the RAID
  • Parity – data storage technique that combines striping and checksum methods.

The combination of those two techniques provides safer and faster data access storage.

RAID 5 advantages:

  • RAID 5 offers data redundancy, so there is a chance for recovery if one drive fails
  • single-parity data storage allows RAID 5 to offer the most usable disk space of any other redundant RAID type
  • performance and disk space features make RAID 5 ideal solution for storing videos, large data which doesn’t require frequent update
  • “Sequential write” performance and disk read performance are in the rank of other RAID levels, and sometimes even superior to other levels.

RAID 5 disadvantages:

  • very poor “random write” performance
  • if you have a large drive failure, rebuilding can take a very long time
  • when two disk fails simultaneously, you lose data
  • in order to improve RAID 5 performance, hardware RAID controllers could include dedicated “XOR Processors”, large write caches, or both

What happens if one drive fails?

If you are facing one drive fail, no need to worry, it can be fixed. In a situation like this, the system will continue to run as usually. The system administrator will be notified that drive has to be replaced. It is extremely important to replace the broken drive urgently to keep the integrity and performance of the system. Now, the question is – how to find out that one of the disks has failed? You will receive a warning message that one of the member disks has failed. RAID will be able to continue writing and reading data but the performance of read operations degrades seriously.
And what if two drives fail at the same time?

Sadly but thru, if two drives fail at the same time, you have a big problem because RAID 5 array is going down and all the array data will be lost. When this happens, the only option to get your data back is to restore them from backup. Remember that RAID is not a replacement for a backup.

It happens that people lose files stored on RAID 5. What is the main reason for that? The answer is formatting RAID 5 volume, mistakenly, of course.

Is there a chance to recover data after formatting RAID 5 volume? That depends whether the data is overwritten which happens by adding some new data. This way you occupy the space on RAID volume. So, if you haven’t added some new data, you have a chance for recovery.

How to recover data if RAID 5 fails?

The first step in process of recovering RAID 5 is to determine configuration parameters:

  • determine the number of disks in the RAID 5
  • determine the disk sequence
  • block size that was used in the array
  • at what offset the array data began
  • what the parity pattern was used in the RAID5

There are two ways to determine those parameters – manually or automatically. If your choice is manually way, you have to be aware that this process requires a lot of time and the most important, special technical skills.

To determine the array parameters manually it is necessary to determine:

  • the disk order
  • block size
  • start offset on the member disk

Unless you are a professional who sees this kind of situation every day, you will spend too much time to solve this problem, so maybe the software is a better solution.

To spare you some time on searching recovery software for RAID 5, we bring you suggestion of 5 solutions you can try out:

ReclaiMe Free RAID Recovery (http://www.freeraidrecovery.com/)
Diskinternals (http://www.diskinternals.com/raid-recovery/)
Runtime (https://www.runtime.org/raid-recovery-windows.htm)
ZAR – Zero Assumption Recovery (http://www.z-a-recovery.com/)
R-Studio Data Recovery Software (http://www.r-studio.com/)

RAID 5E variation

Now, when we said the most important thing you should know about Raid 5, we also have to mention RAID 5E in few sentences.

This is one of the RAID 5 variations. So, what’s the difference between RAID 5 and RAID 5E? First of all, RAID 5E has integrated spare space in order to rebuild the array urgently when one of the member disks fail. Additional space size suits the size of one member disk.

The main advantage of this version lies in write and read speed performance. If we have to highlight the main disadvantage it would be the complexity of rebuild in case of a member disk failure, plus, RAID 5E can be created only using a standalone controller.

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